This invention relates to a sealing plug for blind installation in a suitable hole thereby to plug and seal it, e.g. against high-pressure fluids. Blind installation means that the plug is installed by access through only one end of the hole.
Known types of sealing plugs (e.g. those available under the trademark AVSEAL II®) comprise a stem, passing through a hollow sleeve, the stem being provided with a radially enlarged head and a breakneck. The head abuts the sleeve and the stem, which extends outwards from the accessible side of the workpiece, is pulled, thus drawing the head into the sleeve, causing it to expand radially and thereby seal the aperture into which it has been inserted, until the stem breaks at the breakneck.
A disadvantage of this type of plug is that the portion of the stem which is broken off during installation, i.e. the portion beyond the breakneck, furthest from the radially enlarged head, is wasted, thus incurring disadvantages in terms of material cost and requirement for disposal means. The amount of wastage increases with an increase in the diameter of the plug, as the length of the stem must always be sufficient to allow an installation tool to gain sufficient purchase.
Another disadvantage is that as the plug diameter increases, so the breakneck strength increases. This in turn requires that the pulling jaws and housing of the tool used to install (place) the plug become more bulky, thus limiting the tool access in some applications. Shock loads, noise and re-coil of the stem within the sleeve also need special attention.
A further disadvantage of this type of plug is that whilst it is subjected to anti-corrosion treatment during manufacture, the subsequent breaking of the steel stem on installation of the plug exposes an area which is not corrosion resistant.
An object of the present invention is to provide a non-breakstem sealing plug which overcomes the aforementioned problems.
Accordingly, the present invention provides, in a first aspect, a sealing plug for blind installation in a suitable hole thereby to plug and seal the hole, which sealing plug comprises:
a sleeve,
a nut stem having a shoulder, and a head at least part of which is radially enlarged with respect to the remainder of the stem;
the nut stem being of a material which is harder than that of the sleeve;
the nut stem being internally threaded;
whereby, when the sealing plug is inserted in a suitable hole, with the sleeve entirely within the hole, and increasing force is applied to the stem with respect to the sleeve, axial compression is applied by the shoulder to the sleeve material abutting it, thereby causing the sleeve to deform and expand radially outwardly to engage with the wall of the hole.
An advantage of the present invention is that no material is discarded, thus providing a cost saving over currently known sealing plugs.
Another advantage of the present invention is that the nut stem is entirely corrosion resistant due to the absence of breaking during installation causing a non-corrosion coated surface to become exposed.
The sealing plug preferably includes at least one annular groove provided in the nut stem, into which sleeve material can enter during installation of the plug into a hole. An advantage of the sleeve material entering the grooves is that positive locking between the sleeve and the nut stem is achieved, and the potential for leakage between the nut stem and the sleeve after installation of the plug is reduced, thus improving the efficiency of the plug.
Preferably at least two annular grooves are provided. This is advantageous during manufacture of the nut stem, as a blank nut stem which is having only one groove rolled into it may twist in the machine; rolling at least two grooves will prevent such twisting.
The annular grooves are advantageously asymmetric in profile. An asymmetric groove profile facilitates flow of sleeve material into the groove during installation of the plug, and improves locking between the sleeve and the nut stem once the plug is installed.
The radially enlarged head may be provided with a tapered underside shoulder. This provides the advantage of facilitating the flow of the sleeve material into the first annular groove, i.e. the groove closest to the head, on installation of the plug.
Preferably the radially enlarged head is manufactured by cold heading and is provided with a drive recess, which acts to resist roll-tapping torque during subsequent manufacture of the nut stem.
The invention provides methods of installing a plug into a hole comprising steps of inserting the sealing plug into the hole and applying an increasing force to the nut stem with respect to the sleeve, until in a second aspect the force has reached a predetermined level and in a third aspect the nut stem has been displaced by a predetermined value.
If the installation tool is set to apply an increasing force to the nut stem with respect to the sleeve until a predetermined level of force has been reached, flexibility in the hardness of the nut stem material is possible, without affecting the efficiency of the plug.
Alternatively, if the installation tool is set to apply an increasing force until a set tool stroke, the nut stem will accordingly be displaced by a predetermined amount, which is advantageous if the position of the installed plug is important, e.g. if the nut stem is required to be below, or flush with, the surface of the workpiece. The same plug design suits either of these placing techniques.
The present invention provides, in a further aspect, a method of manufacturing a sealing plug comprising steps of thread-rolling annular grooves onto a nut stem, producing an internal thread in the nut stem, providing a corrosion resistant plating to the nut stem, and crimping a sleeve of a material having a hardness lower than that of the nut stem onto the nut stem.